180 OSTEOLOGY. 





be seen by holding the skull up to the light ; it is convex from side to side, and bears 

 the impress of the gyri of the inferior surface of the frontal lobes of the cerebrum, 

 which rest upon it. In front and at the side .there are a number of vascular 

 grooves for the branches of the anterior and middle meningeal arteries. 



The middle fossa, which in form may be compared to the wings of a bird 

 united by the body, is bounded in front by the curved thin posterior edge of the 

 small wings of the sphenoid ; posteriorly, by the line of attachment of the tentorium 

 cerebelli, extending from the posterior clinoid process along the superior margin of 

 the petrous portion of the temporal bone. The median part of the fossa, which is 

 narrow, corresponds to the fossa hypophyseos and the tuberculum sellae of the sphenoid. 

 It is limited anteriorly by a line connecting the anterior margins of the two optic 

 foramina, and is overhung behind by the dorsum sellse. In this area are lodged 

 the structures which lie within the interpeduncular fossa on the base of the brain. 

 The floor of the lateral parts of the fossa on each side is formed by the great wing 

 of the sphenoid in front, the squamous part of the temporal bone to the lateral side, 

 and the anterior surface of the petrous part of the temporal behind. In the hollows 

 so formed the temporal lobes of the cerebrum are lodged. On either side of the 

 tuberculum sellse are seen the optic foramina ; these pass into the orbital cavities 

 and transmit the optic nerves and ophthalmic arteries. Immediately behind these 

 openings the anterior and middle clinoid processes are sometimes united, so as to 

 enclose a foramen. Through this the internal carotid artery passes upwards. 

 Leading backwards from this, along the side of the body of the sphenoid, is the 

 carotid groove, which turns downwards near the apex of the petrous part of the 

 temporal, to become continuous with the carotid canal, which here opens on the 

 posterior wall of an irregular aperture, placed between the side of the body of the 

 sphenoid and the summit of the petrous part of the temporal, called the foramen 

 lacerum. Through the medial angle of this opening the carotid artery accompanied 

 by its plexus of veins and sympathetic nerves passes upwards. Eunning through 

 the fibrous tissue, which in life blocks up this opening, the greater superficial petrosal 

 nerve, coming from the hiatus facialis, passes downwards and forwards to reach 

 the posterior orifice of the canalis pterygoideus, which is placed on the anterior and 

 inferior border of the foramen lacerum. A small meningeal branch of the 

 ascending pharyngeal artery also passes upwards through this foramen. In front 

 and to the lateral side of the foramen lacerum, and separated from it by a narrow 

 bar of bone, is the foramen ovale ; through this pass both roots of the mandibular 

 nerve, the accessory meningeal artery, and some emissary veins. Somewhat lateral 

 and posterior to this is the foramen spinosum for the transmission of the middle 

 meningeal vessels, together with a recurrent branch (nervus spinosus) from the 

 mandibular nerve. Leading from the lateral extremity of the, foramen lacerum 

 there is a groove which passes laterally, backwards, and slightly upwards on the 

 superior surface of the petrous part of the temporal to end in the hiatus facialis 

 (a cleft opening into the canalis facialis), which gives passage to the greater 

 superficial petrosal branch derived from the ganglion geniculi on the facial nerve, 

 together with the small petrosal branch of the middle meningeal artery. Just 

 lateral to the hiatus facialis there is another small foramen for the transmission of 

 the lesser superficial petrosal nerve. Overhung by the posterior border of the lesser 

 wing of the sphenoid is the superior orbital fissure, the cleft which separates the 

 small from the great wings of the sphenoid, and which opens anteriorly into the 

 hollow of the orbit ; through this pass the oculomotor, trochlear, ophthalmic division 

 of the trigeminal, and abducent nerves, together with the ophthalmic veins as well 

 as the sympathetic filament to the ciliary ganglion and the small orbital branch 

 of the middle meningeal artery. Just below its medial extremity is the foramen 

 rotundum for the passage of the maxillary nerve to the pterygo- palatine fossa. 

 Behind this, and between it and the foramen ovale, the foramen Vesalii may 

 occasionally be seen, through which a vein passes to reach the pterygoid plexus. 



The lateral parts of the middle fossa are moulded in conformity with the 

 gyri of the temporal lobes, but towards its medial part the splitting of the 

 dura mater in the region of the cavernous sinus serves to separate the cranial 

 base from the inferior surface of the cerebrum. As may be seen by transmitted light, 



